marketforce.com

You sign up, and do these mystery shopper assignments. You select whichever ones you want, and the times/dates you want. Most are super easy. I did a McDonalds assignment and followed the directions (ordered 2 meals, 1 drive through 1 walk in) and got re-imbursed for all the food and paid an additional $10.

They have some that you can do in airports too (since we have access beyond security) which can pay $12-15+ per shop. Other stuff too like going into cell phone stores and asking questions about products/service to see if they are giving the right info out.